Dice sweet potato into small 1/2-inch cubes, and set aside. Pour a thin layer of water in a medium pot with and sauté onions and garlic for a minute.

Add a pinch or two red pepper flakes and continue to cook until all the water has cooked off. Add turmeric, 1/4 teaspoon garam masala and stir to coat.

Add 1 cup broth, uncooked lentils, and bring to a boil.

Once boiling reduce to low, cover, and simmer for about 5 minutes.

Add sweet potatoes, bring to a boil again and reduce to low and simmer, until lentils are fully cooked (they expand and the sauce thickens), about 5 minutes more. Check periodically to see if you need additional broth (I tend to add an extra 1/2 cup, but it can vary). Once lentils are cooked and sweet potatoes are fork tender, taste, adding more garam masala as desired.